Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Still, these slithery devices could lead to better, safer, more comfortable colonoscopies to help uncover cancerous polyps.

Cancer of the colon and rectum is the third most commonly diagnosed cancer in the United States and the nation's second most common cause of cancer death. The chances of beating or avoiding this cancer greatly increase with early detection.

Colonoscopies see inside the colon by pushing an endoscope through it — a long tube equipped with lenses and light. The hope is to detect cancerous polyps early.

Although colonoscopies are considered relatively safe, there is a 1-in-500 risk the procedure could damage the colon. Also, the discomfort often linked with pushing the device through the colon can lead to patients calling off colonoscopies before they are complete.

Instead of pushing an endoscope through the colon, researchers now are developing endoscopes that can pull themselves.

"By pulling themselves instead of being pushed from behind, there is no risk for stretching the colonic wall outward and causing painful cramps," explained researcher Dimitra Dodou, a chemical engineer at the Delft University of Technology in the Netherlands.

The main challenge to building such devices involves clutching onto the slippery walls of the colon in a way that does not damage them.

Dodou and her colleagues have found sticky films called mucoadhesives that could help such devices find the traction they need by sticking onto the mucus lining colon walls. These adhesives already find use in techniques for delivering medicines into the body.

"Mucoadhesives are non-toxic," Dodou said. "Moreover, considering that the turnover time of intestinal mucus is estimated in the order of a few hours, eventual leftovers of mucoadhesive will be quickly washed away."

In experiments with snippets of pig colon, the researchers found tubes covered with mucoadhesives could stick well. They also found that different patterns clung better than others. In principle, a device that could pull in or push out segments of itself — thus controlling how much of its adhesive surface it exposed — could grip or let go of the colon whenever appropriate. The device could then wriggle or climb up the colon.

Testing such mucoadhesives in live animals will be the ultimate test, Dodou said. Living colons typically possess more mucous, although the laxatives given before colonoscopies reduce mucus levels, she explained.

Various groups have worked on self-propelled devices for quite some years now, "but none of them uses mucoadhesive," Dodou explained. She and her colleagues suggest new design concepts for devices incorporating mucoadhesives online March 27 in the Journal of the Royal Society Interface.